To close the loop on this, I called Messicks and they helped me find that the ball belonged behind a lever in the hydraulic control valve.
After re-assembling, I still didn't have any pressure. So I drained and found lots of that gasket sealer coming out of the bottom of the unit. Ran for a...
Short story: I pulled the hydraulic cylinder case off of the differential gear case. When I turned the hydraulic cylinder case upside down, a small 1/4" bearing ball fell out. Any idea where this might have come from?
Long story: Bought my first tractor, a used B7300 with 114 hours, from a...